High Resolution Studies of Solar Flares, Active Regions and the Quiet Sun at Centimeter and Millimeter Wavelengths

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This study will continue investigations of solar radio emissions in the millimeter and centimeter wavelength domain, making use of the Very Large Array (VLA) of the National Radio Astronomy Observatory, and the Berkeley-Illinois-Maryland Millimeter Array (BIMA) at Hat Creek. The observed magnetic structure of sunspot associated microwave sources will be compared with model computations to determine the vertical and horizontal components of the magnetic field at specific locations in the low corona. Along with simultaneous soft X-ray observations, estimates will be made of the electron temperature and emission measure and magnetic field in coronal loops. The VLA microwave data along with Spacelab 2 observations of the transition region and coronal lines will be used to study the temperature and density structure of the sunspot atmosphere in three dimensions. Microwave imaging data will also be compared with hard X-ray burst data to compare the power law index of energetic electrons based on radio and X-ray data, to try to reconcile the two indices through appropriate energization mechanisms. Using VLA observations of flares simultaneously acquired with balloon/rocket borne X-ray and UV measurements, flare physics including the origin of microbursts will be studied. Using BIMA, high spatial resolution studies of flares at millimeter wavelengths will be conducted. In particular, the size and spectra of millimeter burst sources, the problem of electron and proton acceleration in gamma ray/millimeter flares and the anisotropy of these flares will be investigated. The relative timing of mm wave vs. cm wave bursts should help distinguish among the possible causes of the simultaneous flare brightening in H, EUV, and hard X-rays. Observations of filaments at mm and cm wavelengths will also be made to determine the nature of bright lanes (at 15 GHz) spanning filaments, and to determine the density-temperature structure of the transition sheath and coronal cavity. Other proposed studies include mm active regions including their polarization and magnetic fields, mapping of coronal holes and quiet regions such as supergranulation network boundaries at mm wavelengths, and to search for acoustic waves in the chromosphere. ***